<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    .contianer{
        width:400px;
        height:400px;
        border:1px solid #000;
        background-color:#e0e0e0;
        display:flex;
    }
    .item{
        width:100px;
        height:100px;
    }
    /* 给第一个容器添加css */
    .item:nth-of-type(1){
        background-color:aquamarine
    }
    .item:nth-of-type(2){
        background-color:red;
        order:1;
    }
    .item:nth-of-type(3){
        background-color:yellow
    }
</style>
<body>
    <div class="contianer">
        <div class="item">1</div>
        <div class="item">2</div>
        <div class="item">3</div>
    </div>
</body>
</html>